Among the medical procedures performed by cardiologists is the angioqraphic examination of a patient's coronary arteries and treatment of those arteries by angioplasty to dilate or remove obstructions (stenoses). The coronary arteries, which branch off the aorta, carry oxygenated blood back to the heart muscle itself to nourish and sustain the heart muscle (myocardium). After the shape and anatomy of the coronary arteries, and the presence and nature of the stenosis has been determined, a special angioplasty catheter, such as a balloon dilatation catheter or other type of angioplasty catheter is advanced to the site of the stenosis to dilate or otherwise treat the stenosis.
A coronary angioplasty procedure involves the use of several catheters, guidewires and related devices. Initially, a guiding catheter is inserted percutaneously into the patient's arterial system, usually by a percutaneous puncture made in the femoral artery in the groin. A guide catheter is advanced, with the aid of a guidewire, upwardly through the patient's aorta to the region of the heart. The distal end (end inside of the patient) of the guide catheter is specially formed so that when it is disposed in the region of the heart, it will assume a shape that facilitates placement of the distal outlet tip of the catheter at the entrance to (the ostium) one of the two main coronary arteries. Typically, the distal tip of the guiding catheter will enter the ostium very slightly so as to be securely positioned. Once the guiding catheter has been positioned, it provides a direct path for subsequent balloon dilatation or other angioplasty catheters that are intended to enter into the coronary arteries to treat the stenosis.
One problem encountered in the use of balloon angioplasty catheters is the obstruction of blood flow from the proximal side of a stenosis to the distal side while the balloon is inflated. Complete occlusion of a coronary artery usually cannot be tolerated for more than about 30 to 60 seconds without incurring serious risk of damage to portions of the heart which receive blood from the occluded artery. As a result, the balloon may be inflated for only short intervals before it must be deflated to permit the resumption of blood flow. It is preferred, however, to dilate a stenosis with the single relatively long continuous balloon inflation as that technique is thought to reduce the risk of restenosis. A number of proposals have been made to increase the time of balloon inflation. One such solution is described in U.S. Pat. No. 4,581,071 (Sahota) which discloses a balloon dilatation catheter having a blood entry port located on the proximal side of the balloon. The port communicates with the main guidewire lumen of the catheter and enables blood to flow from the proximal to the distal side of the balloon even when the balloon is inflated.
The blood flow rate through such a perfusion catheter is determined by the diameter of the flow lumen within the catheter and the pressure difference across the inlet and outlet ports. Typically, a perfusion catheter permits flow, although at a reduced rate. It would be desirable to provide, in such catheters, increased flow rates approaching that when a catheter is not present.
Pumps have been proposed in connection with perfusion catheters to increase the blood flow downstream of the stenosis. Most of the pumping devices are located externally of the patient and withdraw blood from an upstream location, and then return the blood so that it is expelled downstream from the intake openings. For example, U.S. Pat. No. 4,857,054 (Helfer) discloses a perfusion angioplasty catheter with a pump assist in which one-way valves are employed at intake and ejection apertures so that upstream apertures only draw fluid into the catheter while the downstream apertures only permit the ejection of fluid from the catheter. An external pump is employed to eject and draw in blood without having to withdraw the blood from the patient. The blood flow in the Helfer catheter is pulsatile, not continuous, due to the valving arrangement and piston-type pump employed.
Such pump assisted perfusion catheters tend to be complicated, thus increasing the risk of failure.
There is a need, therefore, for a perfusion catheter which increases the flow of blood through the catheter and which is of relatively simple design. Furthermore, in the event of failure, it is desirable that some blood flow through the perfusion catheter be maintained. It is among the general objects of the invention to provide such a perfusion catheter.